Reversible Microcapsule Filter Cake

ABSTRACT

The invention teaches a method of efficiently dewatering a microcapsule slurry to form a water re-suspendable filter cake of microcapsules. The process comprises providing an aqueous slurry of microcapsules dispersed in an aqueous solution; adding an agglomeration agent and dispersing the agglomeration agent into the aqueous slurry; adjusting the pH to a pH level sufficient to agglomerate the dispersed microcapsules; and filtering the aqueous slurry of microcapsules by gravity, vacuum or pressure filtration to thereby form a filter cake of dewatered microcapsules. The agglomeration agent is sodium polyphosphate, sodium tetrapolyphosphate, sodium hexametaphosphate, and/or sodium tripolyphosphate; or with anionic microcapsules or coatings even alkaline earth metal salts such as magnesium chloride, calcium chloride or barium chloride, or even aluminum salt such as aluminum chloride.

FIELD OF THE INVENTION

This invention relates to capsule manufacturing and more particularly tomicrocapsule cake products and processes of manufacturing a microcapsulefilter cake.

DESCRIPTION OF THE RELATED ART

Various processes for microencapsulation, and exemplary methods andmaterials are set forth in Schwantes (U.S. Pat. No. 8,067,089), U.S.Pat. No. 6,592,990), Nagai et. al. (U.S. Pat. No. 4,708,924), Baker et.al. (U.S. Pat. No. 4,166,152), Wojciak (U.S. Pat. No. 4,093,556),Matsukawa et. al. (U.S. Pat. No. 3,965,033), Matsukawa (U.S. Pat. No.3,660,304), Ozono (U.S. Pat. No. 4,588,639), Irgarashi et. al. (U.S.Pat. No. 4,610,927), Brown et. al. (U.S. Pat. No. 4,552,811), Scher(U.S. Pat. No. 4,285,720), Shioi et. al. (U.S. Pat. No. 4,601,863),Kirtani et. al. (U.S. Pat. No. 3,886,085), Jahns et. al. (U.S. Pat. Nos.5,596,051 and 5,292,835), Matson (U.S. Pat. No. 3,516,941), Chao (U.S.Pat. No. 6,375,872), Foris et. al. (U.S. Pat. Nos. 4,001,140; 4,087,376;4,089,802 and 4,100,103), Greene et. al. (U.S. Pat. Nos. 2,800,458;2,800,457 and 2,730,456), Clark (U.S. Pat No. 6,531,156), Saeki et. al.(U.S. Pat. Nos. 4,251,386 and 4,356,109), Hoshi et. al. (U.S. Pat. No.4,221,710), Hayford (U.S. Pat. No. 4,444,699), Hasler et. al. (U.S. PatNo. 5,105,823), Stevens (U.S. Pat. No. 4,197,346), Riecke (U.S. Pat. No.4,622,267), Greiner et. al. (U.S. Pat. No. 4,547,429) and Tice et. al.(U.S. Pat. No. 5,407,609), among others and as taught by Herbig in thechapter entitled “Microencapsulation” in Kirk-Orthmer Encyclopedia ofChemical Technology, V.16, pages 438-463.

More particularly, U.S. Pat. Nos. 2,730,456; 2,800,457; and 2,800,458describe methods for capsule formation. Other useful methods formicrocapsule manufacture are: U.S. Pat. Nos. 4,001,140; 4,081,376,4,089,802, 4,105,823 and 4,444,699 describing a reaction between ureaand formaldehyde; U.S. Pat. No. 4,100,103 describing reaction betweenmelamine and formaldehyde; and British Pat. No. 2,062,570 describing aprocess for producing microcapsules having walls produced bypolymerization of melamine and formaldehyde in the presence of astyrene-sulfonic acid. Alkyl acrylate-acrylic acid copolymer capsulesare taught in U.S. Pat. No. 4,552,811. Each patent described throughoutthis application is incorporated herein by reference to the extent eachprovides guidance regarding microencapsulation processes and materials.

In interfacial polymerization a microcapsule wall from resins such as apolyamide, epoxy, polyurethane, polyurea or the like is formed at aninterface between two phases. Riecke, U.S. Pat. No. 4,622,267, forexample, discloses an interfacial polymerization technique forpreparation of microcapsules. The core material is initially dissolvedin a solvent and an aliphatic diisocyanate soluble in the solventmixture is added. Subsequently, a nonsolvent for the aliphaticdiisocyanate is added until the turbidity point is just barely reached.This organic phase is then emulsified in an aqueous solution, and areactive amine is added to the aqueous phase. The amine diffuses to theinterface, where it reacts with the diisocyanate to form polymericpolyurethane shells. A similar technique, used to encapsulate saltswhich are sparingly soluble in water in polyurethane shells, isdisclosed in U.S. Pat. No. 4,547,429. U.S. Pat. No. 3,516,941 teachespolymerization reactions in which the materials to be encapsulated, orcore material is dissolved in an organic, hydrophobic oil phase which isdispersed in an aqueous phase. The aqueous phase has dissolved materialsforming aminoplast resin which upon polymerization form the wall of themicrocapsule. A dispersion of fine oil droplets is prepared using highshear agitation. Addition of an acid catalyst initiates thepolycondensation forming the aminoplast resin within the aqueous phase,resulting the formation of an aminoplast polymer which is insoluble inboth phases. As the polymerization advances, the aminoplast polymerseparates from the aqueous phase and deposits on the surface of thedispersed droplets of the oil phase to form a capsule wall at theinterface of the two phases, thus encapsulating the core material.Urea-formaldehyde (UF), urea-resorcinol-formaldehyde (URF),urea-melamine-formaldehyde (UMF), and melamine-formaldehyde (MF),microcapsules can be formed by such processes.

Jahns, et. al., U.S. Pat. No. 5,292,835 teaches polymerizing esters ofacrylic acid or methacrylic acid with polyfunctional monomers.Specifically illustrated are reactions of polyvinylpyrrolidone withacrylates such as butanediol diacrylate or methylmethacrylate togetherwith a free radical initiator to form capsules surrounding an oil core.

Common microencapsulation processes can be viewed as a series of steps.First, the core material which is to be encapsulated typically an oil isemulsified or dispersed in a suitable dispersion medium. This medium istypically aqueous but involves the formation of a polymer rich phase.Most frequently, this medium is a solution of the intended capsule wallmaterial. The solvent characteristics of the medium are changed such asto cause phase separation of the wall material. The wall material isthereby contained in a liquid phase which is also dispersed in the samemedium as the intended capsule core material. The liquid wall materialphase deposits itself as a continuous coating about the disperseddroplets of the emulsified oil.

The present invention is an improved method for dewatering microcapsulesand microcapsule slurries. Dewatering a microcapsule slurry isadvantageous for purposes of high solids concentration of materialinputs into commercial processes. Dewatering enables achieving solidliquid separation enabling commercially advantageous and efficienttransport of microcapsules for various industrial commercial processes.

Often, a microcapsule cake is desirable to be formed from a high solidscontent microcapsule slurry. With microcapsule slurries, typically whenthe volume-average microcapsule size is small, such as below about 15 umor in combination with some ultra fine microcapsules of less than 10 um,or ranging even from less than 0.01 to 5 um, the dewatering process canbecome very challenging. Normally, common techniques, such as use offilters and filter aid or microfiltration, might be utilized to attemptdewatering. However, filters plug, and adding filter aid often isineffective and may contaminate the product. The alternative ofmicrofiltration often is not economic and constrained by volume andsolid content.

Another method for filtration involves adding flocculating agents.However, there is no report on how to control agglomeration in a mannersuch that the slurry can be easily filtered without affecting theintended target sized particles. A reversible agglomeration process andmethod of efficiently forming a reversible filter cake would be anadvance in the art, and useful for many practical commercialapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a microscopic image of a microcapsule slurry preparedaccording to Example 1.

FIG. 2 is a microscopic image of a redispersed slurry, of Example 1,redispersed from filter cake.

DETAILED DESCRIPTION

The present invention teaches a controllable, reversible agglomerationmethod and a filter cake produced by such method.

The invention teaches a method of efficiently dewatering a microcapsuleslurry to form a water re-suspendable filter cake of microcapsules. Theprocess comprises providing an aqueous slurry of microcapsules dispersedin an aqueous solution; adding an agglomeration agent and dispersing theagglomeration agent into the aqueous slurry; adjusting the pH to a pHlevel sufficient to agglomerate the dispersed microcapsules; filteringthe aqueous slurry of microcapsules by gravity, vacuum, centrifuging orpressure filtration to thereby form a filter cake of dewateredmicrocapsules. In one embodiment of the method, the microcapsules arecationic and the pH is adjusted to be alkaline, or at least a pH of 8.In a further embodiment, the pH is adjusted to a pH equal to or greaterthan 8 using a caustic material selected from sodium hydroxide,potassium hydroxide, ammonium hydroxide, a hydride of an alkali oralkaline earth metal, sodium hydride, potassium hydride, an alkoxide, ametal amide, or sodium amide.

In an alternative embodiment of the method of dewatering themicrocapsule slurry, the microcapsules are cationic and the pH isadjusted to at least a pH of 5, or to at least a pH of 6, or even atleast a pH of 8, or even a range of pH of from pH 4 to pH 9, or even arange of pH of from pH 4 to pH 10.

In the process of the invention, the agglomeration agent is selectedfrom an alkali metal polyphosphate or an alkaline earth metalpolyphosphate. The agglomeration agent can be sodium polyphosphate,sodium tetrapolyphosphate, sodium hexametaphosphate, and/or sodiumtripolyphosphate.

In at least one embodiment of the process of the invention themicrocapsules typically have a volume-average microcapsule size of 15microns or less, and the microcapsules are cationic chargedmicrocapsules, and in certain embodiments have an acrylate wall.Typically the solids content of the microcapsule slurry is desired to beincreased. A filter cake can be formed by dewatering or filtering themicrocapsule slurry. A slurry of microcapsules can be re-formed byresuspending the formed filter cake into an aqueous solution.

In a further embodiment the method of efficiently dewatering amicrocapsule slurry to form a water re-suspendable filter cake ofmicrocapsules comprises: providing an aqueous slurry of anionicmicrocapsules dispersed in an aqueous solution; adding an agglomerationagent; dispersing the agglomeration agent into the aqueous slurry;adjusting the pH to at least a pH of at least 6, or even to at least apH of 8, or even a range of pH of from pH 4 to pH 10 or greater; andfiltering the aqueous slurry of microcapsules by gravity, vacuum orpressure filtration to form a filter cake of dewatered microcapsules.

Compared to prior art processes, the process of the invention provides astraightforward and efficient method to prepare microcapsule filtercake, particularly of microcapsule with average volume size below 15 um.The technique is functional across a wide pH range and the filter cakemade is reversible, in that the cake can be redispersed.

The microcapsules useful in the process of the invention can be made byany of the various art processes for microencapsulates, including theprocesses described herein in the Description of Related Art section.The dewatering method is widely applicable and is particularly effectivewith polyacrylate microcapsules but not limited to such. The process ofthe invention is particularly useful with cationic microcapsules.

The agglomeration agent useful in the invention to form a filter cake ofdewatered microcapsules is an alkali metal polyphosphate or an alkalineearth metal polyphosphate. Examples of such agglomeration agent includesoldiumpolyphosphate, sodium tetrapolyphosphate, sodiumhexametaphosphate and sodium tripolyphosphate. These materials areparticularly suited for use with cationic or nonionic microcapsules, ormicrocapsules with such coatings.

With anionic microcapsules or anionic coated microcapsules preference isfor an agglomeration agent selected from an alkaline earth metal saltsuch as magnesium chloride, calcium chloride or barium chloride, or evenaluminum salt such as aluminum chloride.

The agglomeration agent is typically used at less than 15%, less than10%, less than 8%, or even less than 5% by weight, based on weight ofthe microcapsule slurry. The agglomeration agent can be used in anamount from 0.5 to 10% by weight, from 1 to 8% by weight, or even from0.25% to 5% by weight based on weight of the microcapsule slurry.

The microcapsule slurry can optionally be combined with other materialsprovided they do not substantially interfere with the effectiveness ofthe agglomeration agent. The optional materials can include any ofvarious surfactant can be added, selected to have less charge than thecationic microcapsules. Other optional materials can include materialsthat influence properties of the microcapsule wall material of themicrocapsules. Such materials can change rheology, influencepermeability, rate of disintegration, or porosity of the wall. Suchoptional materials may include sucrose octyl stearate, polysaccharides,polyethylene glycol, esters of polyethylene glycol, esterified polyol,or saccharide esters. Advantageously, a certain portion of such optionalmaterials are carried with and incorporated in the microcapsule wallsurrounding the capsule core.

Also useful in the process of the invention are microcapsules which arefurther coated with a second coating such as a cationic coating astaught in Popplewell et. al, U.S. Pub. No. 2005/0112152.

The core material of the microcapsules can comprise any of various corematerials include dyes, chromogens, fragrances, phase change materials,solvents, actives such as biological actives, agricultural materials andactives, nutrients, pharmaceuticals, benefit agents, such as perfumes,silicones, waxes, flavors, vitamins, fabric softening agents, well sitelubricants, cement casing hardeners, adhesives, hardeners, curatives andthe like.

Optionally, the microcapsules can be coated with various secondcoatings, such as cationic coatings or coating with polymers such astaught in Smets et. al. U.S. Pat. No. 8,759,275. Such coatedmicrocapsules with encapsulated benefit agents have a high and evendeposition profile across multiple different surfaces. Such encapsulatedbenefit agents and specific classes of amine containing polymers whencombined, provide a high and even deposition profile to themicrocapsules across multiple different surfaces. The process of theinvention can facilitate dewatering of such coated microcapsules.

In one aspect the optional coating on the microcapsules can comprise oneor more polymers selected from the group consisting of polyvinyl amines,polyvinyl formamides, and polyallyl amines and copolymers thereof.Coating can optionally or further include cationic polymers include polyvinyl polymers, having the monomer generic formula —C(R2)(R1)-CR2R3-.Where R1 is any alkanes from C1-C25 or H; the number of double bondsranges from 0-5. Furthermore, R1 can be any alkoxylated fatty alcoholwith any alkoxy carbon-length, number of alkoxy groups and C1-C25 alkylchain length.

In the above formula, R2 can be H or CH3; and R3 can be —Cl, —NH2 (i.e.,poly vinyl amine and its copolymers and N-vinyl formamide, known aLupamin 9095 from BASF Corporation), —NHR1, —NR1R2, —NR1R2 (where R6=R1,R2, or —CH2-COOH or its salt), —NH—C(O)—H, —C(O)—NH2 (amide),—C(O)—N(R2)(R2′)(R2″), —OH, styrene sulfonate, pyridine,pyridine-N-oxide, quaternized pyridine, imidazolinium halide,imidazolium halide, imidazole piperdine, pyrrolidone, alkyl-substitutedpyrrolidone, caprolactam or pyridine, phenyl-R4 or naphthalene-R5 whereR4 and R5 are R1, R2, R3, sulfonic acid or its alkali salt —COOH, —COO—alkali salt, ethoxy sulphate or any other organic counter ion. Anymixture of these R3 groups may be used. Further suitable cationicpolymers containing hydroxy alkyl vinyl amine units, are disclosed inU.S. Pat. No. 6,057,404.

Unless otherwise indicated, all measurements herein are on the basis ofweight and in the metric system. All references cited herein areexpressly incorporated herein by reference.

EXAMPLE 1

To a cationic charged microcapsule slurry prepared by the process ofU.S. Pat. No. 8,067,089 (100 g, solids: 41%, volume median size: (8 um)was added 2.0 g of sodium polyphosphate. Until all the sodiumpolyphosphate dissolved, sodium hydroxide (20%) was added dropwise withmixing to adjust the pH value to 8. The resulting slurry was sticky, butthe sticky slurry was able to be easily filtered by vacuum or pressurefiltration while the non-treated slurry is not able to be filtered. FIG.1 is a microscope image of the agglomerated slurry. FIG. 2 is amicroscope image of the redispersed slurry from the filter cake. FromFIG. 1 it can be seen that the fine microcapsules were agglomerated, butthe larger ones remained integrated. FIG. 2 shows an absence ofagglomerations when the cake was reslurried.

EXAMPLE 2

To an anionic charged microcapsule slurry prepared by the process ofU.S. Pat. No. 8,551,935 (100 g, solids: 40%, volume median size: (10 um)was added 3.0 g of magnesium chloride solution(33%). The processes ofExamples 1 through 4 can be employed. Sodium hydroxide (20%) was addeddropwise with mixing to adjust the pH value to 7. The slurry was stickybut can be easily filtered by vacuum or pressure filtration while acomparable non-treated slurry is not able to be filtered.

The process of the invention is an efficient method for dewatering amicrocapsule slurry. The process of the invention results in a filtercake which is reversible. The filter cake produced according to theprocess of the invention is able to be redispersed from the filter cakeinto an aqueous solution forming an aqueous slurry.

All documents cited in the specification herein are, in relevant part,incorporated herein by reference for all jurisdictions in which suchincorporation is permitted. The citation of any publication is for itsdisclosure prior to the filing date and should not be construed as anadmission that such publication is prior art or that the presentinvention is not entitled to antedate such publication by virtue ofprior invention. To the extent that any meaning or definition of a termin this document conflicts with any meaning or definition of the sameterm in a document incorporated by reference, the meaning or definitionassigned to that term in this document shall govern.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm”.

Uses of singular terms such as “a,” “an,” are intended to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context. The terms “comprising,” “having,” “including,”and “containing” are to be construed as open-ended terms. Anydescription of certain embodiments as “preferred” embodiments, and otherrecitation of embodiments, features, or ranges as being preferred, orsuggestion that such are preferred, is not deemed to be limiting. Allmethods described herein can be performed in any suitable order unlessotherwise indicated herein or otherwise clearly contradicted by context.The use of any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended to illuminate the invention and does notpose a limitation on the scope of the invention. No unclaimed languageshould be deemed to limit the invention in scope. Any statements orsuggestions herein that certain features constitute a component of theclaimed invention are not intended to be limiting unless reflected inthe appended claims.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A filter cake formed by dewatering a microcapsuleslurry to form a water re-suspendable filter cake of microcapsulescomprising: providing an aqueous slurry of microcapsules dispersed in anaqueous solution, wherein the microcapsules are cationic microcapsuleshaving an acrylate wall; adding an agglomeration agent selected from analkali metal polyphosphate or an alkaline earth metal polyphosphate anddispersing the agglomeration agent into the aqueous slurry ofmicrocapsules; adjusting the pH of the aqueous slurry of microcapsulesto at least a pH of 5 to agglomerate the dispersed microcapsules;centrifuging or filtering the aqueous slurry of microcapsules bygravity, vacuum, or pressure filtration to form a filter cake ofdewatered microcapsules.
 2. A slurry of microcapsules formed byresuspending the filter cake of claim 1 into an aqueous solution; andfiltering the aqueous slurry of microcapsules by gravity, vacuum,centrifuging or pressure filtration to form a filter cake of dewateredmicrocapsules.
 3. A filter cake formed by: dewatering a microcapsuleslurry to form a water resuspendable filter cake of microcapsulescomprising: providing an aqueous slurry of microcapsules dispersed in anaqueous solution wherein the microcapsules are cationic microcapsuleshaving an acrylate wall; adding an agglomeration agent selected from analkali metal polyphosphate or an alkaline earth metal polyphosphate tothe aqueous slurry of microcapsules; dispersing the agglomeration agentinto the aqueous slurry; and adjusting the pH of the slurry ofmicrocapsules in a range from 4 to 10 to agglomerate the dispersedmicrocapsules; and centrifuging or filtering the aqueous slurry ofmicrocapsules by gravity, vacuum or pressure filtration to form a filtercake of dewatered microcapsules.
 4. A slurry of microcapsules formed byresuspending the filter cake of claim 3 into an aqueous solution.